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Subject[PATCH 29/33] KVM: MMU: Avoid calling gfn_to_page() in mmu_set_spte()
Date
Since gfn_to_page() is a sleeping function, and we want to make the core mmu
spinlocked, we need to pass the page from the walker context (which can sleep)
to the shadow context (which cannot).

[marcelo: avoid recursive locking of mmap_sem]

Signed-off-by: Avi Kivity <avi@qumranet.com>
---
arch/x86/kvm/mmu.c | 55 ++++++++++++++++++++++++++++++++++++++++----
arch/x86/kvm/paging_tmpl.h | 23 ++++++++++++++----
include/asm-x86/kvm_host.h | 5 ++++
3 files changed, 73 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 3b91227..c0b757b 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -890,11 +890,10 @@ struct page *gva_to_page(struct kvm_vcpu *vcpu, gva_t gva)
static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
unsigned pt_access, unsigned pte_access,
int user_fault, int write_fault, int dirty,
- int *ptwrite, gfn_t gfn)
+ int *ptwrite, gfn_t gfn, struct page *page)
{
u64 spte;
int was_rmapped = is_rmap_pte(*shadow_pte);
- struct page *page;

pgprintk("%s: spte %llx access %x write_fault %d"
" user_fault %d gfn %lx\n",
@@ -912,8 +911,6 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
if (!(pte_access & ACC_EXEC_MASK))
spte |= PT64_NX_MASK;

- page = gfn_to_page(vcpu->kvm, gfn);
-
spte |= PT_PRESENT_MASK;
if (pte_access & ACC_USER_MASK)
spte |= PT_USER_MASK;
@@ -979,6 +976,11 @@ static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
int level = PT32E_ROOT_LEVEL;
hpa_t table_addr = vcpu->arch.mmu.root_hpa;
int pt_write = 0;
+ struct page *page;
+
+ down_read(&current->mm->mmap_sem);
+ page = gfn_to_page(vcpu->kvm, gfn);
+ up_read(&current->mm->mmap_sem);

for (; ; level--) {
u32 index = PT64_INDEX(v, level);
@@ -989,7 +991,7 @@ static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)

if (level == 1) {
mmu_set_spte(vcpu, &table[index], ACC_ALL, ACC_ALL,
- 0, write, 1, &pt_write, gfn);
+ 0, write, 1, &pt_write, gfn, page);
return pt_write || is_io_pte(table[index]);
}

@@ -1005,6 +1007,7 @@ static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
NULL);
if (!new_table) {
pgprintk("nonpaging_map: ENOMEM\n");
+ kvm_release_page_clean(page);
return -ENOMEM;
}

@@ -1347,6 +1350,43 @@ static bool last_updated_pte_accessed(struct kvm_vcpu *vcpu)
return !!(spte && (*spte & PT_ACCESSED_MASK));
}

+static void mmu_guess_page_from_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
+ const u8 *new, int bytes)
+{
+ gfn_t gfn;
+ int r;
+ u64 gpte = 0;
+
+ if (bytes != 4 && bytes != 8)
+ return;
+
+ /*
+ * Assume that the pte write on a page table of the same type
+ * as the current vcpu paging mode. This is nearly always true
+ * (might be false while changing modes). Note it is verified later
+ * by update_pte().
+ */
+ if (is_pae(vcpu)) {
+ /* Handle a 32-bit guest writing two halves of a 64-bit gpte */
+ if ((bytes == 4) && (gpa % 4 == 0)) {
+ r = kvm_read_guest(vcpu->kvm, gpa & ~(u64)7, &gpte, 8);
+ if (r)
+ return;
+ memcpy((void *)&gpte + (gpa % 8), new, 4);
+ } else if ((bytes == 8) && (gpa % 8 == 0)) {
+ memcpy((void *)&gpte, new, 8);
+ }
+ } else {
+ if ((bytes == 4) && (gpa % 4 == 0))
+ memcpy((void *)&gpte, new, 4);
+ }
+ if (!is_present_pte(gpte))
+ return;
+ gfn = (gpte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
+ vcpu->arch.update_pte.gfn = gfn;
+ vcpu->arch.update_pte.page = gfn_to_page(vcpu->kvm, gfn);
+}
+
void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
const u8 *new, int bytes)
{
@@ -1367,6 +1407,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
int npte;

pgprintk("%s: gpa %llx bytes %d\n", __FUNCTION__, gpa, bytes);
+ mmu_guess_page_from_pte_write(vcpu, gpa, new, bytes);
mutex_lock(&vcpu->kvm->lock);
++vcpu->kvm->stat.mmu_pte_write;
kvm_mmu_audit(vcpu, "pre pte write");
@@ -1437,6 +1478,10 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
}
kvm_mmu_audit(vcpu, "post pte write");
mutex_unlock(&vcpu->kvm->lock);
+ if (vcpu->arch.update_pte.page) {
+ kvm_release_page_clean(vcpu->arch.update_pte.page);
+ vcpu->arch.update_pte.page = NULL;
+ }
}

int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu, gva_t gva)
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 136a65d..3d7846b 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -245,6 +245,7 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
{
pt_element_t gpte;
unsigned pte_access;
+ struct page *npage;

gpte = *(const pt_element_t *)pte;
if (~gpte & (PT_PRESENT_MASK | PT_ACCESSED_MASK)) {
@@ -256,8 +257,14 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
return;
pgprintk("%s: gpte %llx spte %p\n", __FUNCTION__, (u64)gpte, spte);
pte_access = page->role.access & FNAME(gpte_access)(vcpu, gpte);
+ if (gpte_to_gfn(gpte) != vcpu->arch.update_pte.gfn)
+ return;
+ npage = vcpu->arch.update_pte.page;
+ if (!npage)
+ return;
+ get_page(npage);
mmu_set_spte(vcpu, spte, page->role.access, pte_access, 0, 0,
- gpte & PT_DIRTY_MASK, NULL, gpte_to_gfn(gpte));
+ gpte & PT_DIRTY_MASK, NULL, gpte_to_gfn(gpte), npage);
}

/*
@@ -265,7 +272,8 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *page,
*/
static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
struct guest_walker *walker,
- int user_fault, int write_fault, int *ptwrite)
+ int user_fault, int write_fault, int *ptwrite,
+ struct page *page)
{
hpa_t shadow_addr;
int level;
@@ -321,8 +329,10 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
r = kvm_read_guest_atomic(vcpu->kvm,
walker->pte_gpa[level - 2],
&curr_pte, sizeof(curr_pte));
- if (r || curr_pte != walker->ptes[level - 2])
+ if (r || curr_pte != walker->ptes[level - 2]) {
+ kvm_release_page_clean(page);
return NULL;
+ }
}
shadow_addr = __pa(shadow_page->spt);
shadow_pte = shadow_addr | PT_PRESENT_MASK | PT_ACCESSED_MASK
@@ -333,7 +343,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
mmu_set_spte(vcpu, shadow_ent, access, walker->pte_access & access,
user_fault, write_fault,
walker->ptes[walker->level-1] & PT_DIRTY_MASK,
- ptwrite, walker->gfn);
+ ptwrite, walker->gfn, page);

return shadow_ent;
}
@@ -362,6 +372,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
u64 *shadow_pte;
int write_pt = 0;
int r;
+ struct page *page;

pgprintk("%s: addr %lx err %x\n", __FUNCTION__, addr, error_code);
kvm_mmu_audit(vcpu, "pre page fault");
@@ -388,9 +399,11 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
return 0;
}

+ page = gfn_to_page(vcpu->kvm, walker.gfn);
+
mutex_lock(&vcpu->kvm->lock);
shadow_pte = FNAME(fetch)(vcpu, addr, &walker, user_fault, write_fault,
- &write_pt);
+ &write_pt, page);
pgprintk("%s: shadow pte %p %llx ptwrite %d\n", __FUNCTION__,
shadow_pte, *shadow_pte, write_pt);

diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
index 44b8925..20597bc 100644
--- a/include/asm-x86/kvm_host.h
+++ b/include/asm-x86/kvm_host.h
@@ -224,6 +224,11 @@ struct kvm_vcpu_arch {
int last_pt_write_count;
u64 *last_pte_updated;

+ struct {
+ gfn_t gfn; /* presumed gfn during guest pte update */
+ struct page *page; /* page corresponding to that gfn */
+ } update_pte;
+
struct i387_fxsave_struct host_fx_image;
struct i387_fxsave_struct guest_fx_image;

--
1.5.3.7


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